The BNF Converter

What is the BNF Converter?

The BNF Converter (bnfc) is a compiler construction tool generating a compiler front-end from a Labelled BNF (LBNF) grammar. It is currently able to generate Haskell, Agda, C, C++, Java, and OCaml, as well as XML representations.

Given a LBNF grammar the tool produces:

• an abstract syntax implementation
• a case skeleton for the abstract syntax in the same language
• an Alex, Ocamllex, JLex, or Flex lexer generator file
• a Happy, Ocamlyacc, Menhir, ANTLR, CUP, or Bison parser generator file
• a pretty-printer as a Haskell/Agda/C/C++/Java/Ocaml module
• a Latex file containing a readable specification of the language

More information: http://bnfc.digitalgrammars.com/

Installation

Some binaries are available at https://github.com/BNFC/bnfc/releases. Installation from the Haskell sources is possible via stack or cabal.

Installation via stack (recommended)

You need a running installation of stack. To install and run the latest version of bnfc from stackage, enter at the command line:

  stack install BNFC
  bnfc --help

BNFC versions in major Stackage LTS snapshots:

Installation via cabal

You need a running installation of a recent version of GHC and Cabal, most easily available via the GHCup. To install bnfc from hackage, enter at the command line:

  cabal install BNFC
  bnfc --help

Installing the development version

To install the development version of bnfc with the latest bugfixes (and regressions ;-)):

  git clone https://github.com/BNFC/bnfc.git
  cd bnfc/source

and then either

  cabal install

or

  stack install --stack-yaml stack-9.4.yaml

(replace 9.4 with your GHC major version, and if you want to build with your installed GHC then add flag --system-ghc).

Mini tutorial

• Build a first parser in 5 min (Haskell backend):

  1. In a fresh directory, prepare a grammar file Sum.cf with the following content:

     EInt.  Exp ::= Integer;
     EPlus. Exp ::= Exp "+" Integer;

  2. Build a parser (in Haskell) with bnfc:

     bnfc -d -m Sum.cf  &&  make

     The make step needs the Haskell compiler GHC, the lexer generator alex and the parser generator happy (all included in the GHC installation).

  3. Inspect the generated files in directory Sum.

  4. Test the parser.

     echo "1 + 2 + 3" | Sum/Test

• Try the C-family backends. (The prerequisites, GNU C(++) compiler (gcc / g++), lexer generator flex and parser generator bison, are usually present):

  bnfc --c   -m -o sum-c   Sum.cf  &&  make -C sum-c    &&  echo "1 + 2 + 3" | sum-c/TestSum
  bnfc --cpp -m -o sum-cpp Sum.cf  &&  make -C sum-cpp  &&  echo "1 + 2 + 3" | sum-cpp/TestSum

• Try the other backends:

  Option	Backend
  --java	Requires Java, JLex or JFlex, and CUP.
  --java-antlr	Requires ANTLR.
  --ocaml	Requires OCaml, ocamllex and ocamlyacc.
  --ocaml-menhir	Uses menhir instead of ocamlyacc.
  --agda	Produces Agda bindings to the parser generated for Haskell.
  --pygments	Produces a lexer definition for the Python highlighting suite Pygments.

Documentation

https://bnfc.readthedocs.org/en/latest/

Support

You can discuss with us issues around bnfc on our mailing list bnfc-dev@googlegroups.com.

For current limitations of bnfc, or to report a new bug, please consult our issue tracker.

Contribute

• Issue Tracker: https://github.com/BNFC/bnfc/issues
• Source Code: https://github.com/BNFC/bnfc
• Haskell coding style guide: https://github.com/andreasabel/haskell-style-guide/
• Some pull request etiquette:
  • Document, document, document! (See style guide)
  • Include test cases that cover your feature.
  • Include changelog entry.
  • More etiquette: E.g. https://gist.github.com/mikepea/863f63d6e37281e329f8

License

The project is licensed under the BSD 3-clause license.

BNFC versions until 2.8.4 released under the GNU General Public License.

Example uses of the BNF Converter

In research:

• NASA's OGMA tool uses LBNF for its grammars, e.g. for a subset of C 99.

In teaching:

• Course Programming Language Technology at Chalmers / Gothenburg University.